1. Field of the Invention
The present invention is directed to a method for controlling the printing in a mail-processing device, particularly in postage meter machines, addressing machines and other mail-processing devices.
2. Description of the Prior Art
U.S. Pat. No. 4,746,234 discloses a postage meter machine with a thermal transfer printer that allows the print image information to be easily changed. Semi-permanent and variable print image information is electronically stored as print data in a memory and read out into a thermal transfer-printing device for printing. This solution was employed in the commercial postage meter machine T1000 offered by Francotyp-Postalia AG and Co. KG and was the first time that an advertising imprint could be changed by pressing a button.
A method and an arrangement for internal cost center printing are available for department-by-department accounting of the value of postage fees consumed with the postage meter machine T1000, with a print image that is rotated by 90xc2x0 or 270xc2x0 being generated by means of a specific print controller (European Application 580 274, U.S. Pat. No. 5,790,768).
Printing business cards, fee stamps and court costs stamps is also possible with the T1000 machine, i.e. generating print images that differ considerably in structure and content from a franking imprint.
A franking imprint usually comprises a postal value stamp, a postmark image with the mail-receiving location and date as well as the aforementioned advertising image and is generated in the aforementioned sequence with, for example, the postage meter machine T1000 by means of printing print columns arranged perpendicular to the transport direction of the item being franked. The overall print column is imprinted by a single thermal transfer printhead. The machine can thus achieve a maximum throughput of franking matter of 2200 letters/hour with a print resolution of 240 dots per 30 mm, i.e. 203 dpi, but the manual feed of franking items limits the throughput of franking items that can be achieved in practice.
European Application 578 042 (corresponding to U.S. Pat. No. 5,608,636) discloses a method for controlling the column-by-column printing of a postage imprint, wherein encoded image information are converted before the printing event into binary signals for driving print elements, whereby the converted, variable and invariable image cannot be compiled until during printing. The decoding of the variable print data and offering of the print data for a complete column in a register ensue by means of a microprocessor. Since the data for the next print column must be edited in the time between two print columns, the computing time of the microprocessor must be in conformity with the proportion of variable print data, the level of franking items, throughput of franking items, and the print resolution. This increases the busload and limits the possibility of printing a franking imprint onto franking items faster. The franking imprint contains postal information including the postage fee data for delivering the letter. Modern postage meter machines enable a security imprint, i.e. an imprint of a specific marking in addition to the aforementioned information. For example, the aforementioned information is used to generate a message authentication code or a signature and a character string or a bar code as a marking. When a security imprint is printed with such a marking, this enables a review of the authenticity of the security imprint, for example in the post office or on the premises of a private carrier (U.S. Pat. Nos. 5,953,426 and 6,041,704).
In some countries, due to the development of postal requirements for a security imprint, the amount of variable print image data that must be modified between two imprints of different franking stamps is very high. For Canada, for example, a data matrix code of 48xc3x9748 picture elements must be generated and printed for every individual franking imprint.
An ink jet printhead can be composed of a number of modules according to the xe2x80x9cnon-interlacedxe2x80x9d principle when the spacings between the nozzles are too large and the number of nozzles of a module are inadequate for printing a printing width of 1 inch (=25.4 mm) with one module given a resolution of approximately 200 dpi. In the ink printhead of the commercial postage meter machine JetMail(copyright), for example, three modules are arranged offset from one another in the column direction of the print image. Each module has only one row of nozzles with 64 nozzles and the modules are arranged slanted to such an extent relative to the print column so that each nozzle row describes an acute angle relative to the transport direction of the materials to be franked. The individual nozzles of each module therefore do not print along a print image column but print along a diagonal that intersects the columns of the print image. As a consequence, pixel offset errors accumulate when the transport velocity is not correctly acquired. Despite acquiring the movement of the franking matter in the transport direction with a high-quality encoder, it is difficult to print a line straight in the direction of the print image column. The individual modules and their offset from one another, moreover exhibit tolerances that arise in the manufacture of the modules. Below a size that is spaced one print image column from the next, a print pulse is supplied with different delay for each module.
A method and an arrangement for tolerance compensation are described in European Applications 921 008 and 921 009, wherein individual printhead data are stored in a non-volatile memory of the printhead and taken into consideration in the print pulse delay. When the pixel offset error exceeds the size by which a print column is spaced from the next, then the binary pixel data in the pixel memory must be changed.
A solution for print image generation for the JetMail(copyright) disclosed by U.S. Pat. No. 5,707,158 and European Application 762 334 describes how the data describing a complete print image are generated and stored before the printing, and is based on a control datafile for field-by-field generation of the print image in a pixel memory before the printing. The print image is defined in image sub-datafiles of the control datafile and is stored as pattern in pixel datafiles. So that the printer device can directly access the pixel data, binary pixel data are not stored in a pixel memory in the sequence along a print image column but are stored as a modified pattern along a diagonal in three sub-regions lying above one another in order to compensate changes in the pattern caused due to the non-interlaced arrangement of the modules. The solution is based on complete patterns of binary pixel data modified dependent on a pixel data change unit, the binary pixel data being intermediately stored in the pixel memory. The print images are compiled before the printing such that the images are read by a print data controller directly from the pixel memory into a shift register, and are serially transmitted to a shift register in the printhead and can be transferred into a latch. The print data controller is realized together with other assemblies in an ASIC (U.S. Pat. No. 5,710,721, European Application 1 154 382).
Some postal demands can be satisfied only with this solution since the microprocessor is supported by the specific pixel data change unit in the ASIC on the Jet Mail CPU board when modifying the image data of variable picture elements. The pixel data change unit is capable of modifying the variable picture elements between successive frankings such that these are stored in the form of binary pixel data in a pixel memory before the printing. The arrangement of the picture elements (pixels) in the pixel memory required for the printing is not beneficial for the modification of picture elements by the microprocessor because of the oblique position of the print modules of the printhead, and would require a high computing outlay. Even given support by a pixel-editing unit, this can only modify a small number of variable picture elements between the imprints.
U.S. Pat. No. 5,651,103 discloses an apparatus and a method for column-by-column printing of an image in real time, wherein variable and fixed image data elements are connected to one another and deposited in a buffer in order to then be used for printing a column. The variable and fixed image data elements are stored in a non-volatile memory, with some of the fixed image data elements being compressed. The print image data for printing each print column are compiled from variable and invariable image data only before they are printed, i.e. the image data for an imprint are not present in binary form in a memory area but in a form that is comparable to the method disclosed by European Application 578 042 for the T1000. The variable image data elements in the non-volatile memory are identified by a controller, and data that correspond to the variable image data elements are transferred to a further controller in order to download the variable and fixed image data elements, unite them with one another, and then print them. The controller proposed for this requires a variable address register for each variable image data element. The number of variable image data thus is limited by the number of address registers.
A postal half-inch ink jet printhead with bubble-jet technology is currently employed in some postage meter machines, this being arranged in a cartridge of, for example, the type HP 51640 of Hewlett Packard and being protected by special means (European Application 1 132 868). 300 nozzles are arranged in two nozzle rows in the half-inch ink jet printhead, these being arranged orthogonally relative to the transport direction of the franking matter and arranged offset relative to one another in the column direction of the print image and in the transport direction of the franking matter (xe2x80x9cinterlacedxe2x80x9d principle).
European Application 1 176 016 A2 discloses ink jet printheads that are specifically protected and drivable for a franking imprint in greater detail. In order to print a franking imprint having a print column length of 1 inch=25.4 mm and having a maximum resolution of up to 600 dpi in the print image column direction with a postage meter machine in one pass of the franking item, two half-inch ink jet printheads are arranged offset relative to one another in the print image column direction and in the transport direction of the franking item. The print image is generated from the print image columns in this orthogonal arrangement relative to the transport direction of the franking matter, with each of the printheads printing a part of the print image column. The machine thus can achieve a high throughput of franking items (5500 letters an hour). The quantity of print image data that must be modified between two imprints is not only very large but also must be made available in a shorter time. When, however, the storing of the binary print image data in the pixel memory for the pixels ensues in the specific sequence in which the pixel data are required for the drive of the two postal half-inch ink jet printheads with bubble-jet technology when printing a column, then the print image is mapped in the pixel memory as a correspondingly modified pattern of binary pixel data. The modification of picture elements by the microprocessor thus becomes complicated again and requires a high computing outlay that can be achieved in the required time only by means of an expensive microprocessor, or the throughout of franking matter is correspondingly reduced.
An object of the present invention is to provide an economical method for controlling the printing in a mail-processing device, which achieves a high throughput of postal items and uses a high-resolution printhead, wherein the variable print image part can be extensive and can be flexible for different postal demands. By simple intermediate storage and address calculation before the printout of the pixel data, the microprocessor responsible for the control of a complete mail processing system should be relieved.
The above object is achieved in accordance with the principles of the present invention in a method for operating a mail-processing device having at least one printhead operable by a print data controller having access to a pixel memory, in which binary pixel data are stored in data words, with a predetermined number of successive data words forming a data string, and wherein the print data controller includes a DMA (direct memory access) controller and an address generator and, for each printhead, a pixel data editing unit. The pixel data-editing unit contains two buffer memories connected to the DMA controller. The address generator and the DMA controller are connected to the pixel editing unit to transfer a data string from the pixel memory into the two buffer memories, with successive data words in one of the plurality of the data strings being alternatingly entered into one of the two buffer memories by the DMA controller, editing the data words stored in the other of the two buffer memories at addresses designated by the address generator. While a data word from one of the buffer memories is being supplied to the printhead for use in printing, storing the next data string in the other buffer memory.
The invention is based on storage of binary pixel data in the pixel memory in a suitable form that makes it possible for an optimally large number of binary pixel data of a picture element to be modified with every command of a microprocessor, and on editing pixel data during printing with an ink jet printhead, and the printhead being supplied with selected binary pixel data grouped in a predefined sequence that is dependent on the type of ink jet printhead (i.e., manufacturer) that is employed.
In accordance with the invention binary pixel data are stored in the pixel memory in the form of data words, with a predefined number of successive data words forming a data string. A presentation of a predefined number of such data strings in a columnar arrangement reflects (represents) the print image to be printed.
A microprocessor-controlled modification of variable binary pixel data in the pixel memory is also a feature of the inventive method, wherein a number of binary pixel data of a picture element in a data word is modified under the control of a microprocessor, with the sequence of the binary pixel data in at least a part of the respective data string coinciding with the sequence of pixels in at least one corresponding print image column that is provided for the printing.
A word-by-word transmission of binary pixel data of a data string from the pixel memory and intermediate storage of the data string in a pixel data editing unit ensue via direct memory access (DMA). The pixel data editing unit undertakes an editing of pixel data during printing, with the ink jet printhead being supplied with selected binary pixel data grouped in a predefined sequence that is dependent on the type (manufacture) of the ink jet printhead that is employed. The groups are formed by a number of binary pixel data whose number and sequence differ dependent on the type of ink jet printhead and its driver unit.
The pixel data belonging to a print image column are arranged in the pixel memory such that the microprocessor can modify variable picture elements in the available time. Since the pixel data for two complete print images are deposited in the pixel memory, the pixel data of the one print image can be employed for printing a franking in alternation and parallel in time with the modification of variable pixel data of the other print image, which is yet to be printed, by the microprocessor. Preferably, two printheads are provided with at least a part of each print image column of the print image being printed out by each printhead. Two printheads in an orthogonal arrangement relative to the transport direction each can print half a column length of a print image column. The two halves of the same print image column are printed offset in time since the printheads are arranged offset in the transport direction of a piece of mail. Moreover, each of the two printheads can have two nozzle rows. Every other pixel on this half column length is a pixel with an even column number of a first print image and is printed by nozzles of the second nozzle row. The remaining pixels with odd column numbers of the print image are printed offset in time on this half column length by the nozzles of the first nozzle row since the first nozzle row is offset from the second nozzle row by a distance in the transport direction, this offset being smaller than the aforementioned offset of the two printheads from one another. A data string of binary pixel data from the pixel memory composed of a number of successive data words yields an identical image of the pixel with even column numbers of the first print image and of the pixels with odd column numbers of a second print image that are printed by a printhead having two nozzle rows. When a number of such data strings stored in the pixel memory is arranged in the sequence by columns, a printing of an identical image of at least a part of the print image printed with a printhead thus occurs, this now being able to be efficiently modified. Using commands and data from a read-only memory, the microprocessor of the postage meter machine generates binary pixel data and stores the data word-by-word in the pixel memory.
Since this arrangement of the pixel data, however, does not yet correspond to the sequence in which the pixel data are required for the drive of the printhead, the inventive print data controller causes the nozzles of the printheads to be driven in a predefined sequence and according to the values of the binary pixel data for printing a print image column. The pixel data required for printing at least one print image column are transmitted by direct memory access into respective buffer memories by (half) words for each printhead and are intermediately stored therein. Using an address generator in the print data controller, the bits corresponding to the individual pixels are transmitted into respective collecting memories for the binary pixel data of the respective printhead from the buffer memory in the sequence required by the printheads, and are then loaded in groups into a shift register with the bit length of one of the nozzle groups, and are subsequently serially transmitted to the drive units that are provided for the drive of the printheads.
Two buffer memories are provided for each of the printheads, with one of the buffer memories being loaded by direct memory access in alternation while the other is being read out in order to transmit the binary pixel data to the driver units. The loading and readout of the buffer memories, which are preferably implemented as dual port RAMs, preferably ensues via separate ports of the buffer memories. After the microprocessor has initialized the direct memory access and started the printing of a print image, an encoder that supplies a pulse rate corresponding to the transport speed of the franking item triggers the loading of the buffer memories and the printing of the pixel data of the data string. The pixel data are arranged in the pixel memory such that the direct memory access can execute a specific number of cycles with one encoder clock in order to thus load the pixel data for the next data string into the corresponding buffer memories. A data string counter is incremented in the print data controller with each encoder clock. The printing is ended when a predefined value has been reached.
An advantage achieved by the inventive method is that a modification of the variable image data in the pixel memory by an economical (relatively inexpensive) microprocessor can be realized during a franking or between successive frankings because the nature of the arrangement of the pixel data in the pixel memory enables an efficient processing of the variable picture elements by the microprocessor and the microprocessor is relieved of the print control. A high degree of flexibility with respect to the scope and the implementation of the variable print image elements is thereby achieved.